Commercial assays for the detection of drugs of abuse in urine change periodically and must be reevaluated for performance. Studies were designed to test the validity of new assays with clinical specimens obtained from drug users under controlled conditions. Healthy male volunteers with a history of chemical substance abuse participated in these studies. Informed consent is obtained and all procedures were approved by the hospital Institutional Review Board. Commercial assays for detection of drugs of abuse in urine were tested for validity with specimens collected under controlled dosing conditions. A variety of drugs of abuse were studied at various dose levels. The results of the assays were compared to GC/MS analysis. In the most recent study, detection times of cannabinoids in urine were measured with cannabinoid immunoassays at 20, 50 and 100 ng/mL cutoffs and with GC/MS. Six subjects smoked a single marijuana cigarette (placebo, 1.75% or 3.55% THC) each week while residing on the clinical ward of the Addiction Research Center. Each urine specimen was analyzed under blind conditions by immunoassay according to the manufacturer's instructions. The following cannabinoid reagents were evaluated Emit( d.a.u. 100, Emit d.a.u. 50, Emit d.a.u. 20, Emit II 100, Emit II 50, Abuscreen Online, Abuscreen RIA, DRI and ADx. All urine specimens were also analyzed for THCCOOH by GC/MS with a 15 ng/mL cutoff. Urinary cannabinoid detection times varied substantially across assays, subjects, doses, and cutoff levels. Detection times were shorter than previously assumed. Mean detection times increased from a maximum of one-half day after the low dose to a day and a half after the high dose with the 100 ng/mL cutoff. Mean detection times were less than one day following the low dose and less than two days following the high dose exposure with the 50 ng/mL cutoff. Mean detection times ranged from one to five days after the low dose and from three to six days after the high dose with the 20 ng/mL cutoff immunoassay. GC/MS detection times were approximately twice as long as mean detection times with an immunoassay cutoff of 50 ng/mL. Differences in sensitivity and specificity between the available immunoassay products affected the efficiency of detection of marijuana use. These results indicate that recent reductions in cannabinoid cutoffs by military and Federally-mandated programs will increase detection times and improve sensitivity, as expected. However, monitoring acute marijuana usage with a commercial cannabinoid immunoassay with a 50 ng/mL cutoff concentration provides only a narrow window of detection of one to two days.